The invention relates to a device for reducing engine-excited vibrations of a drive train, especially a split flywheel, having two device or flywheel elements which are arranged equiaxially relative to one another and one of which is connected or connectable to the engine and the other to the drive train. A spring mounting 18 drivingly connects the device or flywheel elements to one another and is connected to at least a first flywheel element via a first non-positive coupling inserted between an abutment part of the spring mounting and the first flywheel element. A second non-positive coupling, subject to play, is inserted in parallel to the spring mounting between the two flywheel elements, preferably with a non-positive connection reduced in comparison with the first coupling.
A corresponding flywheel is shown in the U.S. patent applicant Ser. No. 829,508, filed Feb. 14, 1986. In this, the masses of the flywheel elements and the forces of the spring mounting are calculated so that, under driving conditions, the vibrations excited by the engine have a frequency in the so-called super critical range, that is to say far above the resonant frequency of the split flywheel. Furthermore, the play of the preferably provided coupling subject to play is made sufficiently large so that, as a rule, it is not used up.
The coupling subject to play and/or the first coupling, which is inserted between the abutment part of the spring mounting and the first device or flywheel element and which, in the arrangement according to the U.S. patent application Ser. No. 829,508, will as a rule have a non-positive connection exceeding the maximum torque of the engine, are only activated in special situations. For example, the situations include when driving suddenly changes from deceleration to acceleration or from acceleration to deceleration, of when, for example during the starting of the engine, the resonant frequency of the split flywheel is excited. In this case, the said couplings act as non-positive connections between the flywheel elements and effectively brake the relative movements between the flywheel elements.
In the split flywheel described in the U.S. patent application Ser. No. 829,508, the abutment part connected to the first flywheel part, via the first coupling, can rotate to any extent in principle against the resistance of the said coupling, so that the torque which can be transmitted between the flywheel elements is limited correspondingly.
U.S. patent application Ser. No. 764,648, filed Aug. 12, 1985, now U.S. Pat. No. 4,662,239 shows a split flywheel, in which the flywheel elements are coupled in drive terms by means of a spring mounting which is supported directly on the flywheel elements or on abutments fixed to these. Arranged parallel to the spring mounting is a stop spring mounting which takes effect only after a movement play between the flywheel elements have been used up. Arranged parallel to the stop spring mounting is at least one coupling which likewise takes effect only after a movement play between the flywheel elements has been used up. In this known arrangement, shocks detrimental to comfort can occur under certain circumstances, when the torques exerted between the flywheel elements, although so high that the play available to the coupling is used up, are nevertheless insufficient to overcome the resistance generated by the activated coupling.
The object of the invention is to provide a constructive alternative to the device mentioned in the introduction, in which the rotatability of the abutment part relative to one of the devices or flywheel elements is limited, without detriment to comfort, especially in the resonant range of the device.
This object is achieved because a further spring mounting is arranged parallel to the first coupling.
As a result of the further spring mounting, which is arranged parallel to the first coupling and which forces the abutment part in the peripheral direction into the region of a center position in relation to the associated device or flywheel part, the non-positive connection of the first coupling can be made relatively slight. This is because the further spring mounting, increasingly tensioned in response to an increasing deflection of the abutment part in relation to the associated device or flywheel part, can, together with the first coupling which seeks to brake the relative movements between the abutment part and the associated device or flywheel part, also absorb high impact moments. On the one hand, the relatively "soft" suspension of the abutment part, which is thereby possible, results in improved comfort, and on the other hand excessively high vibration amplitudes are effectively limited as a result of the interaction of the further spring mounting with the damping caused by the first coupling. In practice, the described effect occurs only during pronounced load alternation between deceleration and acceleration or during the starting of the engine, when, especially during several attempts to start it in quick succession, the resonant frequency of the system is excited for a longer period. As a rule, under all the remaining operating conditions, only the other first-mentioned spring mounting takes effect, together with the coupling subject to play.
Preferably, the first coupling and the spring mounting parallel to it are such that the non-positive connection of the coupling is lower than the maximum engine torque, and the tension of the spring mounting reaches a value corresponding to the maximum of engine torque only after the spring excursion has been partially used up. In this design, as is desirable for a high degree of comfort, the abutment part can yield even under relatively moderate torques taking effect between the device or flywheel elements. On the other hand, impacts exerted on the abutment part are absorbed over a relatively short distance and damped by the spring mounting tensioned increasingly at the same time and by the resistance which the non-positive connection of the first coupling offers to a relative movement between the abutment part and the associated device or flywheel part.
As a rule, the spring mounting parallel to the first coupling is arranged without prestress.
However, it is also possible to have an arrangement with prestress, although this should preferably be lower than the maximum engine torque, so that the abutment part can rotate relative to the associated device or flywheel part even under lower torques.
According to an embodiment of the invention preferred from the point of view of construction, annular discs or annular segments are arranged between the device or flywheel elements on one of the elements in two radial planes located at an axial distance from one another and have apertures which approximately coincide in the discs or segments in an axial view and extend tangentially relative to the disc axis. The apertures receive, in a cage-like manner, the helical compression springs arranged tangentially between the annular discs or annular segments. A further annular disc is arranged axially as an abutment part between the discs or segments, is rotatable relative to the two above mentioned annular discs or annular segments and has cut-outs which surround the end faces of the helical springs.
As a rule, the edges of the cut-outs surrounding the end faces of the helical springs are, in the peripheral direction of the annular discs forming the abutment part, at a distance from one another corresponding to the length of the apertures in the adjacent annular discs or annular segments. Thus, the helical compression springs support free of play, the annular disc forming the abutment part relative to the other two annular discs or annular segments and consequently relative to the first device or flywheel element.
If appropriate, however, it is also possible to have an arrangement in which the distance between the edges is greater, so that the spring effect provided by the helical compression springs is exerted only after a certain play between the abutment part and the associated flywheel element has been used up.
Is is expedient to arrange the helical compression springs in regions of the flywheel elements near the periphery so that, if appropriate, high torques can be transmitted even with relatively weak helical compression springs or those with a relatively low prestress.
The two annular discs or annular segments arranged on one of the flywheel elements can be clamped axially against the further annular disc forming the abutment part, with friction elements or friction lamellae being interposed, in order to form the non-positive first coupling which is inserted parallel to the helical compression springs forming the further spring mounting. In this arrangement, virtually no additional parts are therefore required for the said coupling.
In an especially preferred, independently inventive design of the device described above, the play of the coupling subject to play is limited resiliently at least in one direction of rotation of the flywheel elements relative to one another. This resilient limitation is provided particularly for that relative direction of rotation which occurs between flywheel elements in response to increased deceleration.
The benefit of such an arrangement is that the damping caused by the coupling subject to play takes effect without a torque jump. In particular, when the play of the coupling subject to play is used up to an increasing extent, an element limiting the play resiliently is first tensioned increasingly, until the coupling subject to play is activated and yields at a sufficient torque. Thus, resilient limitation of the play prevents the relative movement between the flywheel element from stopping abruptly, when the torques exerted between the elements on the one hand are sufficiently high to use up the play, but on the other hand do not exceed the non-positive connection of the coupling subject to play.
The arrangement of the coupling subject to play can be such that it has at least one annular lamella which is arranged on the first flywheel element with play in the peripheral direction and interacts with friction surfaces, friction lamellae or the like arranged on the other flywheel element, and which cooperates with one or more springs which are supported on the first flywheel element or on a part connected to the latter and are activated only after the play has been partially used up.
For this purpose, resilient pins can be arranged on one of the flywheel elements and engage with play recesses extending in the annular lamella tangentially relative to the axis of the annular lamella.
For this, the pins appropriately have a fixed core and a ring which is arranged on the latter with elastomeric material interposed and which engages into a particular one of the recesses.
If appropriate, extensions, bolts or the like can be arranged on the annular lamella or on one of the flywheel elements and, after the play has been partially used up, come up against a spring supported or arranged on the one flywheel element or the annular lamella, for example against a bow spring. If appropriate, the spring end interacting with the extension or the like can have a slot or the like surrounding the extension or the like and arranged tangentially relative to the axis of the annular lamella.
A further preferred embodiment is characterized in that the annular lamella is arranged axially between annular discs or annular segments which are arranged on one of the flywheel elements and which retain in a cage-like manner, by means of apertures or the like provided in the discs or segments, helical springs or the like arranged between these discs or segments tangentially relative to the disc axis. The annular lamella includes cut-outs surrounding the end faces of the helical springs by means of radial edges, the distance between which is greater than the length of the above-mentioned apertures or the like in the peripheral direction.
Thus, if appropriate, according to the difference between the distances between the radial edges and the length of the apertures of the like, the annular lamella can move, without the helical springs seeking to counteract the movement of the annular lamella.